Semiconductor substrates are used in a wide variety of applications. One such application is in the formation of micromechanical electrical system (MEMS) devices. As the need for increased complexity of the physical structure of MEMS devices has increased, a number of different shaping processes have been developed. Three major categories of shaping processes are bulk micromachining of silicon, surface micromachining, and deep reactive ion etching (DRIE). Each of these processes has unique benefits and capabilities. For example, DRIE processes provide very steep sidewalls which are useful in minimizing device footprint.
Typically, the processes used in shaping a substrate allow for highly complex shapes to be defined in the plane of the substrate. For example, circles, squares, and lines can be defined by processes such as lithography on a substrate surface and then etching processes can be used to remove material not covered by the lithographic layer. The shape of the substrate in a cross sectional plane, however, is constrained by the particular material removal process. Thus, DRIE provides substantially vertical sidewalls while chemical mechanical polishing (CMP) provides a substantially horizontal surface.
Curved shapes in the cross sectional plane, however, are less deterministic. For example, etching can be used to generate a curved shape. Control of the etching process, however, is difficult. Thus, precise location and shape of a curved sidewall using an etching process is problematic.
What is needed, therefore, is a method for providing a curved shape in a cross sectional plane of a substrate. A method that can be used to provide precisely positioned and dimensioned curved shapes in a cross sectional plane is also needed.